The objective of this proposal is to develop the transition metal- mediated reductive coupling of two unsaturated centers into a general, catalytic, stereoselective method for formation of carbon-carbon bonds within carbocyclic and heterocyclic organic target molecules. A notable advantage of the transition metal-catalyzed reductive coupling reaction is that enantioselective transformations can be effected with an inexpensive, achiral stoichiometric reductant in the presence of a substoichiometric quantity of a chiral transition metal complex (asymmetric catalysis). Such a process will be a valuable alternative to reductive coupling protocols which employ an expensive reducing agent in stoichiometric quantities. We propose to study the chemistry of the titanium oxometallacycles and related species formed by reductive cyclization (e.g., azametallacycles, zirconium metallacycles) with the goal of developing useful synthetic protocols for the stereocontrolled synthesis of highly functionalized carbocyclic and heterocyclic compounds. In particular, we will develop new catalytic methods for reductive cyclization.